text:
How do I plan for my PPL checkride which will involve a diversion?
My CFI has told me that in my checkride I will begin a planned cross country flight and will be diverted to another airport shortly into the flight. My question is, how do I effectively plan for this? I am unable to get for example NOTAMS, weather predictions, runways and their lengths etc. for the airport I'm going to (because I don't know what it is)
From what I have read I will be acting as PIC on the checkride and as such I don't feel like I can comfortably satisfy CFR 91.103 when I don't even know where I will be flying to.

This thread should be a great source of tips and tricks :)
The way to think about this is to think about the purpose of being asked to divert during your checkride.
What the examiner will be looking for is not that you have all of the information for every possible airport you might be asked to fly to.  The examiner is wanting to see that if you had to divert unexpectedly for whatever reason, that you are able to do this safely.  That's the bottom line.
In order to do this, you should start working on the problem during your ground planning, and for the purposes of your checkride, this will be no different to planning any other flight.
Plan for your alternate.  You should have charts, frequencies etc and of course, enough fuel.  Your examiner is not going to ask you to divert to somewhere when you reach your destination, it's going to be somewhere en-route.
As part of any good plan, you are going to familiarise yourself with possible diversions along the route.  If you had an urgent situation (not a dire emergency where nearest available is the only choice) requiring you to divert when you were flying solo after you gained your license, where would you go?
This doesn't mean that you need every possible piece of information for every possible airport but it does mean:

Do I have enough fuel to make possible diversions?
Do I have charts on board covering the areas to the left and right of my plan?   - Have I folded my charts so that it's easy to see what possible diversions there are easily?
Do I have Jeppesen (or whatever) on board and is it up to date?
Have I checked the METARs and NOTAMs for anything significant for those likely diversions.
Do I have my E6B or other planning tool and do I know how to use it fully?
Do I know what ATC agencies I would talk to along the route if I need assistance, even if flying in uncontrolled airspace?

In your notebook for the planned flight, write down the likely diversion airfields with their key details.
The list above should be part of any plan, not just for your checkride.
One of the key things you're going to need to figure out is "how long will it take me to get to the diversion"?  In order to know this, you're going to need to know the wind at the altitude you are going to be flying at. The way I handled this was to draw a circle on my chart, marked with the wind at altitude, then the corresponding ground speed already worked out on my E6B and written into the circle for each cardinal and mid-cardinal point on the compass rose.  You can glance at this little chart to instantly see that if, for example, the requested diversion needs me to fly a heading of 320, I will be doing 86 kts for an airspeed of 100 kts.  This saves you having to actually use your E6B in the cockpit to do this.  Mark off 0, 45, 90, 135 etc.
If you think about it, doing this in planning will prepare you for any *sensible" diversion you might be asked to make.
When it comes to the time of the diversion, the primary thing your examiner is looking for is do you get "aviate, navigate, communicate"?
The second thing the examiner is looking for is "can you safely divert from en-route"?
If you have planned thoroughly, and you follow aviate, navigate, communicate, then almost by definition, you will safely divert.
So your examiner suddenly says, OK, see that completely unexpected giant sandstorm ahead, you need to get down soon.  Please divert to "Mark Watney- Space Pirate" airport.
Avoid the single, most important thing in this whole exercise at this point.  Do no go into heads down mode.  It's easy to do if you are unprepared.  Your head should be down for at most 15 seconds.  Do each thing one step at a time, then scan and lookout.  If you are well prepared and planned, then not going heads down will be easy.
You now need 3 things immediately - everything else can come later.

What heading do I need to fly?
How long will it take me to get
there?
Can I make it?

For the heading, grab your chart, find the airport, then take a rough heading you need.  You don't, at this stage, need to be super accurate.  Within 10 or 15 degrees will be good.  The important thing is to begin flying to towards the diversion.  You can get the ruler out and refine your heading once you've got the initial diversion sorted out.  Don't forget to aviate.  Keep your head moving, keep your scan and lookout going.  When you set up for the new heading and turn on to it, remember the gross error check as you roll out.
How long will it take?  Again, you don't need to be super accurate.  Grab a quick measure of the distance from the chart and your ruler.  Then look at that wind chart you prepared earlier.  Get your estimated ground speed.
Can I get there?  You should know the aircrafts' fuels consumption numbers so do the quick calculation in your head.
During all of this, remember to aviate at all times.  Also, remember to conduct your normal en-route and turn check lists.
Now it's time to communicate.  If you are in controlled airspace, let them know you've diverted then start looking for who you might need to talk to along your diversion and get the next frequencies into the box.
When you are safely flying towards your destination, you can start to do some more detailed in-the-air planning to refine your estimated heading and fuel use if needed.  You can also now deal with "do I have the NOTAMs and METARs" I need?  It's OK not to have them all for every possible airport (you should have them for the most likely ones) because you can always call up ATC.  That's one of the reasons they are there - to help pilots dealing with unplanned contingencies.
Remember, the examiner is looking for prior planning and aviate, navigate, communicate.  If you do this, I hope that you will see that the unexpected diversion is not actually that scary.
This is primarily a planning exercise, not a flying exercise.  Arrive in plenty of time.  Recognise that every minute you spend planning will reduce your stress and workload in the air and aim to be ready to go, twiddling your thumbs and itching to get airborne, 15 minutes before your planned time to walk to the aircraft.
You might notice that I've repeated myself a lot.  That's deliberate.  Prior planning and aviate, navigate, communicate it what this is all about.
Good luck!

Thanks a lot for taking the time to write such a detailed response! This is exactly what I was looking for. One small additional question. Do you think the examiner would think its cheating to use the GPS to get distance + true course quickly and then use your wind trick?

You're welcome. Is GPS cheating? Yes!  Your examiner will likely not allow you to use GPS or some software flight planning tool - even if it is approved use.  They want to know that you can plan in advance and can use dead reckoning navigation if needed.  What would you do in real life in a total electrical failure or, you find that the batteries on your tablet have died, or it has crashed, just when you need it most?

One thing I learned is to use my pen instead of a ruler to measure the distance: place the pen on the chart with the tip at the diversion destination, and your fingers holding the pen at your current position. Then lay the pen against a line of latitude. Since each division on a sectional is 1 nm, you can easily measure the distance.  You can derive ETA now by knowing that at 90knots, you travel 1.5nm (tick marks) per minute, and at 120 knots, 2nm (tick marks) per minute. eg 35nm should be 17-22 minutes ETA.

Contrary to what @Simon said, it's not cheating to use GPS. Examiners want to know that you can use every available tool at your disposal. Can the GPS die? Sure, and (s)he'll likely ask what you would do if the GPS is inop. But if you have it and don't use it, you can get dinged too.

@hashinclude  What jurisdiction?  In CAA land, at least when I did my test some years ago, portable GPS was explicitly forbidden.  If fitted to the aircraft, yes the examiner would expect you to demonstrate that you could use it but you can bet it would "fail" not long into the flight.  The first navigation leg was required to be conducted using dead reckoning.  https://publicapps.caa.co.uk/docs/33/srg_lts_Stds%20doc%2019H_V2_Sept12.pdf.  However, as you can see in the current test conduct documentation, GPS is permitted for the diversion leg but remember, the examiner can switch it off.

The answer is: you can't plan this.
This is done to see how you react while in flight to a non-planned diversion, and can happen anytime in real life.
It's used also to evaluate how you manage stressful situations, how you manage both flying the plane and searching through the documentation to find the plate of the new destination.
Of course, this means you should have with you all the required maps and approach plates for all the airfields in the vicinity of the planned path (wether its paper or in an electronic device).
And even if you don't have some required information, the tester will ensure you are able to safely proceed when encountering any unexpected situation, and thats the bottom line of any pilot.

See my answer.  I absolutely disagree that you can't plan this.

@Simon Well, I don't really see the point: you and I are more or less saying the same thing, but your answer is far more complete. My first sentence is just a bit exagerated, of course you need to plan ahead, but the goal is also (IMHO) so see how you react to something you didn't plan...

Your CFI has likely sent candidates to your examiner in the past and will have a good idea of her tendencies on checkrides. Use this advance intel to your advantage, but play along and act surprised in the moment. The diversion is supposed to be unplanned.
One really useful tip to prepare for a diversion is to build a wind card. Ask your briefer for the winds aloft at your planned altitude, and use your E6B or other flight computer to compute groundspeed and wind-correction angle for courses of 000, 090, 180, and 270, i.e., the heading you will hold to travel along the ground in the four cardinal directions and how rapidly you’ll do so along each.
For example, see below. I suggest arranging them along the four points rather than a flat list.

Winds: 220@12
Airspeed: 115 knots
North

GS: 124 knots
WCA: -4°

South

GS: 106 knots
WCA: +4°

East

GS: 122 knots
WCA: +5°

West

GS: 108 knots
WCA: -5°

Your diversion course will not likely be due north. However, having done the math up front for the cardinal directions, interpolating between the two nearest your actual diversion course will provide rapid, straightforward estimates.
I had to fly my diversion under the foggles as a demonstration of dead reckoning. The DPE also “failed” the GPS but flipped it from the map page to the nearest airports page. I gave my estimated heading and time beforehand, but I was also giving position calls on the diversion airport’s CTAF using the distance I could see on the GPS. It wasn’t a big deal, but I had to fly to another airport — tiny and tucked in behind trees, so hard to find — to demonstrate dead reckoning.
Instead of being eager beaver on the radio, I should have quietly used the resource to my advantage. Prepare thoroughly but also act a little surprised rather than having canned responses all pre-planned.

Since this is going to be your PPL check ride you wont need approach plates or any of that. A current sectional is what you need. You can plan for this, just as you would if you are planning a cross country later. You look along your planned flight path and select possible airports to divert to in the case of an emergency. I carried a small ruler. You should have that or use a pencil for distance measurement. My examiner wanted to know course, distance, time en route and fuel burn to get to the airport. If you did a solid flight plan you will already know the possible diversions and have an idea of how to answer the questions. Before you turn to your new course make a show of checking the area for other aircraft. Clearing turns are not out of the question. Remember, your examiner is looking for your attention to safety as well as your ability to fly. He knows you can fly a plane or you wouldn't be taking the check ride. He is looking for your ability to fly safely. You can use the instruments in the plane. If you have GPS, punch up the airport and hit the direct to button. If he doesn't like that, he'll tell you to figure it out on paper. You can still use an E6B. SAFETY SAFETY SAFETY. A good plan is a safe plan and that includes possible diversions. The problem is you are looking at a chart, trying to figure out your course etc. and you are not looking outside. He is looking for that. Your answer does not have to be immediate. You are busy flying the airplane first, figuring out your diversion second. Once you have your course you can turn to your new heading, get trimmed, then figure out the rest.
The diversion test is not difficult if you have planned ahead. Good luck on your ride!


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Why is Emirates not considering buying or leasing used A380s?
Airlines such as Korean Air are retiring their A380s. They are struggling to find buyers/lessors. In such a scenario, Emirates could easily obtain used A380s at cheap prices.
Is Emirates not leasing used A380s because of the costs involved in re-configuring of the aircraft? Since the A380 is an expensive aircraft, I feel that even with added costs in changing seating layout and maintenance of aged aircraft, it might be economical to consider used planes.
We have to also consider that since its the same aircraft, customers won't notice any difference in service or comfort.

This very well might be an opinion question, but maybe Emirates has publicly released statements as to why they aren't buying used A380s.

If the customization allowed by Airbus is comparable to what Boeing allowed on the 747, a major problem might be that cockpit instrumentation is different, switches are different, limitations different, etc. If so, that would mean pilots would have to be trained for those differences, not an inconsequential concern. Having flown for carriers that had only airplanes purchased from other carriers, it's a real problem. And dispatchers would also require additional training. And flight attendants might also.

Emirates has just agreed to buy 20 more A380s (with an option for 16), but very few other airlines are interested because they carry too many passengers. That makes them very inflexible for an airline on which routes they can fly, and be profitable. To be profitable, you have to fill almost all the seats, every flight, all year round. There are only so many routes that can do that, and Emirates have already sucked a lot of those passengers up on their existing routes, flying through their Dubai hub. There aren't a lot more passengers to attract, so they do not need more A380s.

"The A380 is not made for every route, but it is ideal for high-traffic routes, high-volume routes that are congested or where there are flying constraints,"

(From "Bigger isn't always better: Why the A380 super jumbo is struggling to take-off").
And, if there is a slight downturn in passenger numbers, there's not much you can do with an A380, but fly it a bit empty. However, if you have smaller aircraft, you can run two medium aircraft when the demand is heavy, or one medium and one small one when the demand is a bit less, or just one small one, in the off-season. But... you can't do that with an A380. You either go 3/4 full, or not at all. So, it's inflexible for route planning.

Qantas originally order 20 of the double deckers but decided to only take delivery of 12. According to Joyce, the Dreamliner offers the airline more flexibility and lower financial risk especially on routes with inconsistent or seasonal demand.
“If we were to fly two (236-seat) 787s tail-to-tail, the per-seat cost would be less than the (486-seat) A380,” Qantas CEO Alan Joyce said in an interview.

(From "We may have just witnessed the end of the A380 super jumbo").
Airlines don't buy aircraft just because they have the latest technology. Airlines buy aircraft that will have a lower cost per seat-mile. This should be an aircraft with the latest technology, but, if that technology comes in an aircraft with more seats than you can fill, then the cost per seat-mile isn't as good as it should be, and may be higher than a smaller, older aircraft.
So, simply, the A380 is too big. It makes an airline put all their eggs in one basket, and only Emirates had the routes and traffic to buy it in any quantity.

Emirates has recently agreed to buy more A380!

You're correct, I hadn't seen that report since the news from the Dubai airshow (Nov 2017) when Emirates basically invited Airbus along, then left them jilted at the alter. Maybe it was all a ploy, or maybe Airbus turned them around. Either way, it doesn't change the fact only one airline really has the routes and traffic that can use such a large number of passengers. In fact, it reinforces the points above. It's still not selling in quantity, and would be interesting to know if Airbus will actually break even on its development costs. Cheers.

Several reasons come to mind. Emirates just announced two days ago that they have concluded an A380 deal for 20 more firm orders and options for another 16. I suspect these orders will “fill” existing current slots. It is true that several airlines have begun to decommission some A380’s from service. The lease of these aircraft have expired and the airline, (i.e. Singapore Airlines) has decided not to renew the lease or buy it out. It should not imply that Singapore Airlines did not make a profit using the aircraft, it probably did.
Instead, it is very likely that Singapore management believed the future profitability was going to be limited based on current economic conditions such as rising oil prices and stiff competition on some long-haul routes. Another factor is that Singapore Airlines still has 4 more A380’s to be delivered from its original order it placed in 2009.
Those that are being rotated out of service will possibly have a new A380 take their place. So I am not clear how the question can imply that the airlines are not making a profit with the A380.

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Why are passenger and cargo airplane noses manufactured separately from fuselages and then put together?
I was wondering why the fuselage of a passenger airplane is not built along with the nose? It might be difficult to build fuselage and wings together as one unit, but nose is a small part. Then why is it made separately?

Do you mean just the radome (it is quite obvious there; it is completely different material), or the whole forward section (this depends on the manufacturer how many parts of the fuselage are built separately before final assembly)?

Yes, the radome.

Well, then it should be kinda obvious. The radar must be mounted under it before it is attached to the fuselage and that is done fairly late in the manufacturing process.

See if you can find a picture that show what you're asking about. If you're not sure how to embed the picture, just edit your post and paste the link in, someone will come along and embed it for you. Realistically, though, the entire aircraft is made up of a whole lot of sub-assemblies that are then put together to make the final whole, the same way cars, ships, and many buildings are. The "nose" is just another sub-assembly that's tacked on in the final assembly process. You can see some of the Airbus process here.

Here is one really good reason why they are separate components it happens quite often actually.

Maybe you think the fuselage is built in a single piece, but this is not the case. Different sections may be manufactured at different locations. Moreover there are bulkheads at the ends of the fuselage, to deal with pressure differential. The radome is unpressurized and outside this volume.

A radome, or nose cone, is essentially a structural cover serving a different purpose than the fuselage. These are made separate because they a special material invisible to the radar mounted beneath them. They are different shapes or sizes depending on the customer specific component they cover (radar antennas) and can be easily removed or replaced.
The radome serves two essential purposes. 1) It covers electronic equipment mounted to the forward bulkhead of the fuselage to protect it from weather, or from view. 2) It acts as an aerodynamic cover for the leading edge of the aircraft.
https://en.wikipedia.org/wiki/Nose_cone

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text:
Are there any electric ultralight aircraft?
Are there any electric, FAR part 103 aircraft?
FAR part 103 aircraft are unique in that they don't need a license to fly.

Please don't confuse something that doesn't need a license with something that doesn't need training, because nothing is further from the truth. Unfortunately there are many people no longer around with the same attitude. If you are really serious about flying, renting a 150 and getting your PPL or even SPL isn't a bad thing.

Note that not everyone can make the requirements for a medical certificate; flying under the more restrictive part 103 limitations on vehicle specs and operating rules greatly reduces the risk to other people of your making a mistake or having a medical problem in flight. That said, GET SUITABLE TRAINING BEFORE FLYING SOLO -- I intend to!

ElectraFlyer offers a Part 103 legal trike, and at least as of two years ago, had a flying prototype of a more conventional designed single-seat Part 103 legal ultralight.
Realistically, given the weights of engines and batteries compared to the weights of the Rotax or similar engines usually used on ultralights, it's possible to turn many Part 103 designs into electric power, provided you're willing to do the engineering work yourself. For a fairly extreme example, see Dale Kramer's eLazair, a twin electric motor conversion of the Lazair ultralight that retains its Part 103 status.


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How can I calculate the moment coefficient around the center of gravity?
Hi guys I was wondering if you could help me with the following problem:

Wing surface area= 260m2 (sw)
MAC= 6.608m (cw)
horizontal stabilizer surface area=69.5m2 (st)
distance from the cog till the aerodynamic center of the horizontal
stabilizer=30m (lt)
change in downwash angle vs angle of attack de/da=0.5
distance from wing til aerodynamic center (hacw) = 26% of mac angle (hacw)
of the wing is 0.12 per degree (aw)
angle of the stabilizer = 0.07 per degree (at)
downwash stabilizer at an angle of attack of 0 is e0=0
moment coefficient of the wing in the aerodynamic center is
Cmacw=-0.04
CoG=31%

Calculate the moment coefficient around the CoG(Cmcg) of the entire airplane when the angle of attack is 3 degrees and the angle of the stabilizer is 1.5 degrees aircraft nose up.
I know the answer which should be Cmcg=-0.022 but I have no idea how it is calculated.
I am sorry, what i did was the following: I calculated the tail volume coficiency which is 1.213564, the position of the neutral point being it 0.61396. I am trying to use the following formula:
$C_{mcg}=C_{macw} + a_w  a_w (h-h_{acw}-{a_t\over a_w} V_h (1-{\Delta e\over\Delta a})) + a_t V_h (i_t+e_0)$
when filling in I do the following
$-0.04+a_w A_w (0.31-0.26-{a_t\over a_w} 1.213564 (1-0.5) + a_t × 1.213564(i_t+e_0)$
for aw and at I am not sure to use the 0.12 and 0.07 or do it times 3 and 1.5 for the degrees. it seems to be angle of the stabilizer but I am not sure. e0 I think is 0 but again not sure.

I am sorry, what i did was the following:

@Jay I tried making your maths slightly more readable, don't know if I succeeded, feel free to revert the edit if it's no longer accurate.

@falstro thanks, as you can see I am as green as they come. I'll do better next time!

Yeah, no worries this MathJax stuff looks pretty much like gibberish if you don't know LaTeX (markup format mostly used for scientific papers)

$-0.04+0.12*3 (0.31-0.26-{0.07\over 0.12} 1.213564 (1-0.5) + 0.07 × 1.213564(1.5+0)=-0.022$
note that aw=the slope of the liftcurve and Aw=the absolute angle of attack.


text:
Can anyone identify this tri wing twin engine WW1 plane
Can anybody identify this WW1 or earlier plane? This tri-wing plane has two engines, most others I have googled have only one.

I see three props... Probably, three engines, two tractor props and one pusher...

Flying spaghetti monster?

Gianni Caprioni's 1918 Ca 4 triplane bomber, shown here with Caprioni and three companion aircraft. It has a twin boom tail and a pusher prop in the center pod, so it is a triengine triplane.

source

Probably a Caproni Ca.42. Six were acquired by the RNAS, which became the RAF in April 1918. (A service number of 2xxxxx indicates a man who transferred in from the RNAS, incidentally, so this fits.)
The squadron which operated these, after renumbering, was No. 227 RAF; WP suggests this was part of 67 Wing, though I can't find a clear source for this elsewhere.

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text:
Where can I find the best site to learn aircraft design on a small scale?
I am undergraduate student still trying to figure out a lot about Aerodynamics and aircraft design. I am learning how to design rc planes.
So the thing I know the weight of my plane which is between 700 gm to 1000 gm and velocity which is 13 m/s.
I just know the basics that is the lift formula and other fundamentals. I want to know how to design a nice fuselage for my plane and also how to keep balance in my plane. I seriously need help and also there are courses where you learn all this, but they ask for heavy cash.

Hi Sai. I will let the community decide on this, but I have to warn you that this question is a bit borderline for us, as it asks to locate external resources (leaving aside that "best" is opinion-based) and generally these questions are not accepted here.
Please take a moment to go through these help pages:
https://aviation.stackexchange.com/help/dont-ask
https://aviation.stackexchange.com/help/on-topic

Are you open to learning from paper books as opposed to web sites?  There are a number of very good books on aerodynamic design oriented toward model size aircraft, typically sold through hobby supply outlets.

Yes !...I am to books too!

As Federico explained, this question is a bit borderline on 3 areas: asking for external resources (off topic), asking for best resource (opinion-based), asking for RC planes (most of us fly real planes here, although aerodynamics still applies). I hesitated for a few minutes but ultimately decided to vote to close. I hope the existing answers, as well as this related question here, covers what you need.

It's not a website, but it's totally worth buying: Dan Raymer's Simplified Aircraft Design for Homebuilders (ISBN 10: 0972239707  ISBN 13: 9780972239707) is applicable to RC aircraft and has the best ratio of comprehensive coverage to beginner-friendliness of any resource I know.

13 meters per second calculates out to around 30 mph.
At 1 kilogram, you should have no problem whatsoever
getting it in the air.  Models at this weight generally land at around 8 to 15 mph and are capable of around 50+ mph at full throttle.  I would start by looking at classic airplane designs like the Piper Cub.
One of the best sources of more info would be your
local hobby shop.
Bob


text:
Do swept back wings affect the moment of inertia of an aircraft enough to be relevant for the roll response?
I have studied that swept back wings help in delaying the shock waves formed on the wing, but also to my understanding I feel swept back wings reduce the moment of inertia (like for example a ballerina dancer where she spins so easily when she keeps her hands close to her body).
This in turn helps in improving the roll response which is an advantage to a fighter jet. So is my understanding correct?

does this answer your question? https://aviation.stackexchange.com/q/9287/1467

Actually no.... maneuverability wise I did get my answer...also wanted to know what I had thought is correct or not

Could talk more about what you believe to be true re: swept wings. - are you talking about wings that can be moved ? an if not, then we need a point of reference - swept wings reduce the inertia relative to ... what? ...a plane with the same lift/speed characteristic? ...a plane with the lift/area characteristic?

A wing has three basic design parameters—span, chord and sweep—which are all independent of each other.
Span is always measured along the perpendicular axis of the whole aircraft and chord is always measured along the longitudinal axis. So pivoting the wing around its root will change all three parameters and affect the properties that depend on them.
When designing the aircraft, you choose area (span times chord) to give you the needed amount of lift, then span to give you the desired minimum lift-to-drag speed and sweep for transsonic capability and/or stability. So you should be comparing swept and unswept wing of the same span and area, and those somewhat obviously have the same moment of inertia in roll.

The Bell Airacobra was designed with the ballerina or ice skater analogy in mind by centering the weight as much as possible.  Amazingly, the Dunne swept wing
biplane (with rudders at the wing tips too) was
rejected as being TOO STABLE for military use!
Sweeping the wing was originally used for issues
such as adjusting center of lift.  The B17 production design, with its huge new tail and lots of weight aft
compared to the prototypes, may have benefited from a
little sweep.  Adding the chin turret on the G model
may have helped with weight balance considerably.
Swept wings can be also found in the Tiger Moth biplane.
It was serendipitously discovered that sweep also helps delay the onset of shock waves as one approaches
Mach 1 and became very popular at the dawn of the
supersonic age. This is a famous story.
Not as often told, but equally true, is making the
wings THINNER, as on the Spitfire, also helped a lot.
But as far as ballerinas, it turns out that roll rate
is generally improved with shorter wings as on the F16, but weight distribution remains important.
PS Birds do pull the inside wing in while turning, which also helps them slip-turn with their tails.

F-104 had wing leading edges so thin that they presented a cut hazard to ground crews. Designed for supersonic age.

Yes, for a low-speed aircraft, swept wings are useful to avoid problems with the center of gravity, to move the wing spar into a more convenient location, or to improve the sideways view from the pilot's position. This increases the  longitudinal static stability of the aircraft as done by Anglo-Irish engineer John William Dunne.
The slight rearward shift of the aircraft center of gravity is caused by the rearward shift of the wing weight. Indicated by the cross-hatching is the distance between the center of gravity and the center of lift. A small amount of longitudinal stability is highly desirable, but the large increases with sweep angle can cause reductions in aircraft maneuverability and large increases in trim drag. Another issue with variable swept wings is reduced pitch stability due to additional lift and fuse interference. They tend to suffer from lower yaw stability. Also one should note that the mechanism for variable swept wing increases weight of the aircraft.
You also have to keep in mind that variable swept wing aircrafts were designed in an era that focused more on speed rather than maneuverability. The ideology changed after realising the data that showed how much time these aircraft spend in supersonic speeds and hence the focus shifted from speedy to more agile aircrafts.

How exactly does the longitudinal location of the CoG affect the roll response, which is what this question is about?

It depends what's the profile for the aircraft in question. Although all the fighter aircraft have relaxed stability around lateral axis to provide increased maneuverability. As @Robert DiGiovanni mentioned in F-16, important factor for CG is also weight distribution just having swept back wing won't alone shift the COG to but there are other factors also. OP needs to mention what is exact config.

I feel swept back wings reduce the moment of inertia (like for example a ballerina dancer where she spins so easily when she keeps her hands close to her body).

If you take a straight wing and sweep it back, yes the moment of inertia is lowered.

This in turn helps in improving the roll response which is an advantage to a fighter jet. So is my understanding correct?

No, it is not an advantage to a fighter jet, because planes place aileron control surfaces outboard from the fuselage (closer to the wing tips), as you sweep the wing back, the arm from the aileron to the fuselage gets smaller, resulting in a smaller moment being applied. As a result, your roll response will be smaller if you swept the wing back, despite the lower moment of inertia.
The moment of inertia doesn't get much smaller - fuel tanks are located either in the fuselage or inboard in the wings, so most of the mass stays pretty much where it was before, as the outboard wing sections are empty and light.
The F-14 deployed straight wings during dogfights for better maneuverability, sacrificing top speed.

You can “take a straight wing and sweep it” in different ways. If you simply rotate it around the root, you'll extend the chord and reduce the span, but if you try to preserve most properties and shear it maintaining the chord, you'll maintain span too and the moment of inertia in roll won't change (the moment of inertia in pitch will increase in both cases).

There is more than just the moment of inertia involved in the roll response, and the response itself is more than just one figure.
Let's consider something like a swing-wing airplane, where nothing changes except for the sweep angle. Furthermore, we'll assume standard ailerons control, which rarely happens on the actual swing-wing aircraft.
The difference in inertia will be noticeable but not that great: most of the mass is still in the fuselage. (Especially this applies to real swing-wings, where it is difficult to carry the fuel and ordinance under the wing). That said, the contribution of the wingtips will reduce as a square of the reduction of the wingspan.
But there are also forces involved. The most significant ones will be the ailerons (control) moment and the roll damping.
If we have ailerons near the wing tips, the moment from them will reduce linearly with the wingspan. At the same time, roll damping depends on the square of wingspan and so will reduce more. Damping reduction is the most drastic effect: the wing is almost exclusively responsible for it. This fundamentally differs airplanes with the proverbial ice-skaters and ballerinas.
Overall, in a typical case, with a longer wingspan you may get faster initial response (ignoring aeroelastic effects, which may reverse the trend even here), but significantly slower sustained roll rate.
Aircraft with short stubby wings may get in trouble due to their fast roll rate, even if (and partly because) their ailerons do not seem that efficient: see inertia coupling.

In a swing-wing airplane, not only does the sweep angle change, but the span and chord change with it.

...and the moment of inertia, and roll damping, lots of things. Of course. But all that is the consequence of changing the sweep angle; only this latter is the "degree of freedom". That's what I meant.

Except in design, span, chord and sweep are all independent degrees of freedom. So while a swing-wing only has one degree of freedom, it is not just sweep, it is a combination of the three.


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How to calculate the power required during transition from VTOL to fixed wing?
In a VTOL, I have calculated the power required for take off and cruise which was not difficult at all. Between take off and cruise, there is a phase where the VTOL has to transition by tilting the rotors from 0 to 90 deg. I am finding it hard to calculate the power required for this transition. I feel this is very important because it consumes more power than take off since it is creating lift (hasn't reached the minimum velocity for the lift requirement) for balancing weight and also needs to provide thrust for forward motion.
Given to me are:

Rotor parameters

number of rotors
Rotor diameter
rpm
number of blades

Fixed wing parameters

span and chord (rectangular wing)
lift and drag coefficients

What are the factors considered to calculate the power required for transition?
Please note: Make as many assumptions/approximation as you like. I just want a simple formula for a basic understanding.

The VTOL is a tilt rotor type with ducted fans

Are your rotors ducted or unducted? What kind of VTOL is this? Depending on the specific configuration, the transition and cruise phases would need to consider the disk loading like in a helicopter. If, however, the wing is large and the disk surface is negligible, then you can treat the rotors as vectored thrust sources and just use high school trigonometry to solve the transitory phase.

Ok let's say I assume my wing to be large and disk area negligible.....How do I calculate the power now?....Because I feel integration is involved from 0 deg to 90 deg.

Another comment if I may.  The maximum power requirement will be to produce its own weight in thrust plus enough thrust to hold altitude in a downdraft while in vertical flight.  If you set your safety limit at say 20 feet per second, a drag calculation could be made for the plane being raised at this speed vertically based on area presented in vertical flight.  You may find this is more than enough for transition to horizontal.

Like Hobbes said. For instance, after take-off, tilt the thrust 10° forward. The cosine is 0.98 so you only lose 2% of propulsion lift. The sine is 0.17, so forward thrust is 0.17 * total thrust.
The craft will speed up until aerodynamic drag = forward thrust:
$$ T = D = C_D \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$
$$ V^2 = \frac{2 \cdot T}{C_D \cdot \rho \cdot S}$$
Then tilt to 20° where you have sin(20) = 34% of the propulsive thrust pointing FWD and 94% pointing UP, etc.
Note that it is usual to express the drag equation relative to wing area S.
A simple real-time approximation in a spreadsheet would look like underneath. 9810 N thrust pointed back 10 deg results in sin10*9810 = 1703 N forward thrust, which takes about 300 seconds to speed up the craft to 97 m/s. Of course, because of the aerodynamic lift the craft climbs, changing AoA and creating induced drag etc. The simulation should be extended with reduction in rotor thrust proportional to aerodynamic lift. But I hope the gist of things is clear enough.

.
.

But you should take into account the lift generated from the wings also right

Yes you should, which you can calculate once you know the speed. The forward thrust accelerates the craft, causing both wing lift and drag to rise every second until T = D.

So I have studied the procedure you have followed.What if we just keep constant thrust and tilt the angle from 0 to 90. The problem what I am facing is that when we do that , we reach the desired stall speed at an angle of 6 deg and so what do I do to completely rotate it to 90 deg without creating extra lift.

Reduce the thrust proportionally.

Then you would be decelerating in forward flight right.

No. At take-off, all thrust is required in vertical direction. Then vector some of it in horizontal direction, like you said at 6deg until you reach stall speed. Then slowly tilt the vector more horizontally, while slowly reducing thrust. Thrust required for normal flying using wings is way less than thrust for lift.

The lift of the wing is proportional with the square of the aircraft speed, see the lift formula. That tells you how much vertical thrust you need at each speed.
The vertical thrust of the rotors depends on the cosine of the tilt angle, horizontal thrust depends on the sine.
The horizontal thrust leads to the speed you can reach at that tilt angle, but you need the total drag of the aircraft to calculate this. That's info you don't have, it seems.
Integrals give me headaches, so first I'd calculate these parameters for let's say 10-degree increments in tilt angle and plot these, perhaps a curve will become apparent in the plot.

For the drag ,I have the drag coefficient and the area right......
and after finding out the parameters,how do i calculate the the total power required for transitioning.......How's the plot going to help me

The plot will identify where the peak in power demand is, and you can either measure the height of that peak from the plot, or calculate from the speed indicated in the plot. You have lift and drag for the wing, but do you have drag info for the fuselage?

How do I calculate the drag when I do not know the velocity at that angle


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Why would an airplane fly in parallel, straight, closely spaced lines?
I am not an expert with this kind of stuff and I seek an expert explanation.
Is this pattern related to a ground scan?

possible duplicate: https://aviation.stackexchange.com/q/30443/1467

Hello, welcome to Aviation.SE. maybe you have seen the above mentioned posts. Maybe you did not. It would be very helpful if you could explain, why these posts do not answer your question. Have fun!

Possibly N338MM (Tenax Aerospace).


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Why don't airliners have turboprop engines instead of jet engines?
I know the q400 is one of few airliners that has a turboprop engines. I know that some military airplanes use turboprop engines so why don't many airliners use them?

I believe this could answer your question:
http://aviation.stackexchange.com/a/1817/9907

Most military airplanes are jets, not turboprops.

The question shows little or no prior research. A search returns the typical answer "Because propellers become less efficient as the speed of the aircraft increases, turboprops are used only for low speed aircraft like cargo planes. High speed transports usually use high bypass turbofans because of the high fuel efficiency and high speed capability of turbofans." (source). Some have speculated the fuel price increase may lead to widen the use of turboprop.

Turboprop engines are used in ATR aircraft too. The main reason the airlines are not using turboprop engines are,

They are not as efficient as jet engines for high altitude long distance flights. This is why all the turboprop aircraft are used of short haul flights.
Their efficiency decreases as the speed increases above Mach 0.6~0.7.In comparison, Boeing 747-8 cruises at around Mach 0.85.(Their efficient (cruise) speed is less compared to jet aircraft(~700-750 kmph versus ~880-840 kmph). This adds quite a bit of travel time to long haul flights.
The cabin (and outside) is significantly quieter in case of turbofan engines when compared turboprop engines. This is an important issue in case of civil aircraft where the noise (and vibrations) affect passenger comfort.
The turbofan engines produce a lot more thrust compared to turboprop engines, for a given size(the turboprop engine output is measured in shaft power though). This makes them unsuitable for large aircraft.
The huge propellers in the large turboprop aircraft require long landing gears which increase the weight and complicate the maintenance.

The largest (and fastest) turboprop powered civil aircraft, flew slower and lower than jet aircraft from comparable era. It wasn't known for its comfort either.

Point 1 and 4 are utterly wrong.

@Peter Is point 1 wrong even given point 2 (which seems to say that a turboprop will take longer to fly a certain distance at efficient speeds)?

@cpast: That depends on how you define efficiency (see the answer about the efficiency of the Concorde engines). But if we take the fuel per seat-mile (no speed involved), the turboprop clearly comes out ahead. If we take transport performance (lowest cost for seat-miles per hour), the competition is closer, but still in favor of turboprop

Point 5 is not so black and white. A high wing design like ATR-72, An-70 or An-148 can accommodate practically any propeller size and don't have long gears.


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Are two twin-jet flights more efficient than one quad-jet flight?
Ignoring for this question the issue of flexibility for the airline, would it be more (fuel, cost) efficient to have a single flight with a 4 engine plane than to have two flights with 2 engine planes.
I imagine, that 2 flights of twin-engine planes move more dead mass than a single flight of a quad-engine plane with the same capacity.
As one concrete example, say one A-380 @ 15000 km and 650 passengers vs. two A-350 @ 15000 km and 325 passengers each.

Some further clarification

The two (full) twins carry the same number of passengers as the (full) quad
The two twins and the quad fly the same (long haul) distance
Efficiency can be either consumed fuel, the cost or any other interesting parameter.

What is your metric for efficiency ? Fuel consumption ? Operating costs ?

I suppose under the assumption of equal engine size?

A Bae 146, a quad jet, seat 70 passengers. A A350XWB can seat 348, and yet is a twin.

This question is too vague and subjective to be answerable.

The way you set up the comparison is unrealistic. The one four-engined airplane will win hands down - as long as the two twins are small enough. But that is not how it plays out in reality. Please think about asking a more realistic question.

You may rephrase your question. I think it is more about plane capacity than number of engines. E.g. pro/cons/ of flying one big plane or two smaller with half the capacity?

Would there be a twin & quad combination with roughly the same age?

This has been answered before here. For the same distance and numbers of passengers smaller aircraft are more efficient. The only reasons for larger aircraft are range and runway usage.

Why don't you simply compare 2 A319 and 1 A340-300 on a medium range route or 2 767-300 and 1 747-400? British Airways used the same RB-211 engine on both types, however, I suppose their 747-400 are not exactly carrying the double amount of passengers compared to 767.

@ElectricPilot: The two vs. one Airbus comparison sounds interesting, although the A340 would have plenty of range left. Also the two vs. one Boing comparison sounds interesting. Do you have any numbers on fuel consumption per seat?


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Why do we have to do an alternate brake check during preliminary cockpit preparation?
As part of the preliminary cockpit preparation in my company’s older A320s we have to perform an alternate brake system check but not in the newer ones as per FCOM Normal procedures as below. I found out that there is a system difference but didn’t fully understand could someone please explain the difference?

ALTERNATE BRAKING SYSTEM
  Note: The purpose of this check is to
  verify, before the first flight of the day, the efficiency of the
  alternate braking system (absence of “spongy pedals”).
  Y ELEC PUMP
  pb-sw....................................................................................................CHECK
  OFF
  CHOCKS..............................................................................................................CHECK
  IN PLACE PARK BRK
  handle.......................................................................................................................OFF
  BRAKE
  PEDALS.....................................................................................................................PRESS
  Apply maximum pressure on both pedals.
  BRAKE PRESSURE (on BRAKE press
  indicator).................................................................CHECK
  Pressure must build up without delay symmetrically on left and right
  sides for the same application simultaneously applied on left and
  right pedals. With full pedal deflection, the pressure must be between
  2 000 and 2 700 PSI.
  BRAKE PEDALS................................................................................................................RELEASE
  PARK BRK
  handle........................................................................................................................ON
  The parking brake must be on during the exterior inspection to allow
  the flight crew to check brake wear indicators.

Different braking systems, see Alternate Brake Check on A320/321

I still didn’t understand? This is the answer which my company has provided. But I don’t understand the logic.                                                 The aircraft is without electrically controlled Alternate Braking Control Unit (ABCU). Alternate braking in turn is controlled by BSCU.As a consequence of this during the preliminary cockpit preparation, it is necessary to check the alternate braking system as it is not automatically monitored.

In older A320s, the alternate braking system unlike the normal braking is not computer controlled. The alternate braking is controlled by auxiliary LP pressure distribution lines and is entirely mechanical. When you press the brakes with normal braking unavailable, pressure is sent by the hydraulic lines which closes off the automatic selector valve and opens a dual valve through which the hydraulic pressure is sent for braking.
Interestingly, even when normal braking is available, the pressure is sent through the alternate pressure lines (powered by yellow hydraulic system) and it continues to supply hydraulic pressure and the dual valve also opens. But as the larger side of the automatic selector valve is placed on the side of the normal braking line, the green hydraulic pressure overcomes the yellow pressure and keeps the yellow side closed preventing the fluid reaching the dual valve. This way, the alternate braking is inhibited.

The alternate brake check we do in the preliminary cockpit preparation is to check whether the dual valve operates and functions as it should. As the entire system is mechanical, it is good practice that we check the working of the alternate braking system before the first flight. You do not want a situation where you lose breaking due to a sticky valve, do you?
Why this procedure is not required in newer A320 models is because, the alternate braking is no longer controlled with auxiliary distribution lines. Like the BSCU (Brake and steering control unit) computer that controls the normal braking, now there is a separate computer called an ABCU (Alternate braking control unit). With this, the dual valve which was previously controlled manually is now controlled by the ABCU. When the green hydraulics or the normal braking is not available, the ABCU orders the dual valve to open and when normal braking functions as it should the valve is kept close.

https://web.facebook.com/A320Theory/photos/a.207337252739678/790898894383508/

On the old system the switching between the normal braking using the green circuit  to the alternate braking using the yellow circuit is done by an automatic switching valve pressure dependant (Automatic selector).The alternate system being very little used, it happened the valve did not switch from green to yellow when loosing the green circuit
please refer to the old system here below
http://www.a320dp.com/A320_DP/landing-gear/images/braking-schematic-d.jpg
On the new system the alternate brake is activated by a specific computer(ABCU) decision and is automatically tested by the computer at power up as soon as the hydraulic pressures are available, please refer here below to the new circuit
https://m.facebook.com/A320Theory/posts/normal-brakingnormal-braking-is-obtained-when-the-green-hydraulic-pressure-is-av/790898894383508/
Hope this has been useful and explains why it was very important to do the testing on the old system


text:
Why do we see a reduction in temperature in a wind tunnel by increasing the velocity, but in a real flight it's the opposite?
In a real flight, when the speed of an aircraft increases, we see an increase in temperature too. So that at high Mach numbers the surfaces of the aircraft will be very hot.
Now I have encountered this issue that in a wind tunnel and for a test model it works in reverse order. So that the flow velocity in the tunnel is increased, the temperature of the test model surfaces will reduce, and at high Mach numbers, we need to use heaters to prevent freezing.
My question is this: is this fundamentally correct? If it is, what's the reason for this difference?

I believe the reason is that the air is cooled while compressed in the high pressure reservoir before the high speed wind tunnel.
When moving air is stopped (as happens around the leading edges of the aircraft), its pressure increases (per Bernoulli's principle) and since the compression is adiabatic (no heat exchanged (yet)), its temperature also increases. The final temperature is called Total Air Temperature (or stagnation temperature).
For flying aircraft, the total air temperature is its original temperature plus the increase due to compression by the leading edges of the aircraft. That's why the leading edges heat up in supersonic flight. The other sides don't, the air is not stagnant around them.
However, for wind tunnel, the air was already stagnant in the high pressure reservoir before it—high-speed wind tunnels usually pre-compress the air, because compressors can't produce supersonic speeds. It this reservoir it cools down, and then as it accelerates down the wind tunnel, it adiabatically expands, reducing its temperature well below ambient. It returns to the temperature in the reservoir at the leading edges, but around the rest of the model the air is not stagnant, so it has the lower temperature of the flow.

Hides your answer is perfect save one small detail.  Compressing the air in storage will heat it (PV = nRT).  Once compressed, it will cool to ambient temperature, but is still compressed.  When it is released (as you explained), the pressure (there for temperature) will drop.  Lining up pressure cylinders and using the cooling effect in sequence is how they first made liquid oxygen!

Hides?  @Jan Hudec!  Sorry.


text:
RR Ultrafan: Why the dramatic change of fan blade design?
The Rolls Royce Ultrafan prototype has been in development for a few years and has usually been seen in the media with very distinctive curved leading edge design as such:

However, this week (December 2022) RR have officially put it into testing, and has what appear to be more conventional looking blades:

Have they abandoned the curved set? or just trying several sets?
Source of images: Rolls Royce Ultrafan images

@qqjkztd They are completely different.

https://flic.kr/s/aHsjXZFoNS If you look at the collection of images of the Ultrafan, it appears as if there are not two, but three different types of fan blades. Also, the fan with less swept blades is covered extensively in these images.

I think they're all the same blade. It's just the angle and scale which they are photographed accentuates the curve. It's a 3D shape, so the front-to-back variation is less obvious when looking at the engine straight on.

I'm trying to change the images in the question to ones that were taken from the same angle to better highlight the differences; they're not the same blades at all.

The problem with asking this sort of question about this sort of technology is that the designs and design choices are proprietary, and RR are unlikely to comment much. If pushed you might get a comment about the evolution of the design through testing and development, but what they won't tell you is that the curved leading edge is dramatically better aerodynamically, but impossible to manufacture in volume. Or the reverse. Information like that is not something they want to hand to their competitors.

I think engineers have taken over from the marketing department ;-)  More seriously, the latest iteration of the ultrafan has blades which are some 18% longer than the previous one (i.e. some 40% more area). I suppose that structural reasons played an important role in limiting the curvature of the leading edge.

They've been running it on the benches.... centrifugal forces fairly quickly straightened out the artistic curves the PR folks had in. :-)
[The above is not entirely in sarcasm - they probably have found having a blade which has a high degree of curvature along the aeroline and along the structural centre of rotation lines hasn't played as well as they'd hoped.]

Any design will go through many iterations, they obviously have been trying many blade designs. As for the merits of this design I would expect that information to be proprietary, and therefore you are unlikely to get an answer that isn't generic.

Thanks for your comments all :-)
I note that the "latter" blades, although having a far less wavy leading edge, do have a form of hump in them...
I have a few friends that work at RR, will ask if anyone has any info.


text:
DA 40 NG - Diesel option OAM 40-370
Diamond DA-40 NG Manual did say that to use Auto Diesel (EN590), OAM 40-370 must be installed. Does anybody know or have experience on this OAM 40-370 requirement?
I cannot find this document on the Diamond Website

what exactly do you need help with? as it stands your question is a bit vague and we cannot really help you.

OAM 40-370 is a STC, I think the OP is asking what modifications are required for auto diesel @Federico.

@GdD or they could be asking where to find the text describing this OAM [I cannot find], or they might be asking who can do the modifications [does anyone have experience]

You can easily find this out for yourself by searching on the OAM.
This leads to Diamond Aircraft service bulletins relating to the change.
Work instruction
AFM
Software notice
Looks from these that it requires 3 things:
2 placards relating to the different engine operation temperatures, and potentially a software upgrade to the engine management system (depending on the version currently installed).

According to the work instruction, you also need to install check valves if they are not already installed.

Thank you all for the assistance. I got info from Diamond that OAM 40-370 is factory document.

@AbdRazakMohamadzin you're welcome. Glad I could help. Blue side up and have fun.


text:
What are the differences between PC and professional simulators?
It looks like there are a differences between the models used in the schools and the simulators you can run in a PC .
I'm curious to know the differences and price of both type of simulators.
I thought that the one in the schools were just simple PC simulators.
What simulator can I use to practice basic helicopter stuff?

You still need some number of hours training with an instructor in a real helicopter.  I think it's still 40hrs, minimum.  The marginal benefit of a really good helicopter sim is probably not worth it.

Please [Edit] your question to indicate what kind of simulator you have in mind. There's a massive difference between a full flight simulator (probably out of reach of all but the largest flight schools and above) and something you can run on your home computer with no extra hardware (which the question Dave pointed you at discusses to some extent), and those are only the extremes on the scale.

There are couple of simulators to chose from: FSX/P3D (not that good for actual helicopter training), X-Plane (very good for training) and the new Aerofly FS 2 (also very good for training). The last two can actually save you a lot of money on flight lessons if you invest in a collective lever, cyclic stick and pedal usb controllers. Not only can you skip the "getting to know the controls", you might actually be able to hover yourself in your first real lesson. With all of these you still need the 40hrs minimum but probably no more than that. Totally worth it.

Voting to re-open since Microsoft Flight Simulator is not the only option.

Even if this is not a duplicate question, isn't this off-topic because it's a shopping question?

DCS (Digital Combat Simulator) has a very good flight model for some of its helicopters. You would definitely need a joystick, rudder pedals, and a throttle as well in order for it to contribute to your flying skill.

The main difference is in the flight dynamics model. A PC simulator can be realistic, but who is to say that it is? A professional simulator must show to the authorities (EASA,FAA etc) that the modelled behaviour matches flight data.
There are several authorisation levels, from very basic to zero-flight-time. Even for the basic devices, the authorities want to make sure that only correct cues are generated and that there never will be any negative training habits formed by the simulator user.
PC-based programs can teach students where the buttons and indicators are, what to push, which instrument to monitor far what etc. Some of them are accredited by the authorities, more info in answers to this question.

There are four types of aviation training devices: Basic Aviation Training Devices, Advanced Aviation Training Devices and Flight Simulators that are regulated under §61.4 and full flight simulators (FFS) and flight training devices (FTD) that are regulated under 14 CFR part 60
The BATD and AATD often use the same software that you can use on your home computer e.g. X-Plane. The difference is that they have received a Letter of Authorization (LOA) from the FAA certifying that the software and accompanying peripherals satisfy the rules regarding BATDs and AATDs. You can read more about it in AC_61-136B
Here’s the relevant part for a BATD like FlyThisSim.

B.3.1 General Control Requirements. The following items are required
  for all ATD approvals.
B.3.1.1 The aircraft physical flight and associated control systems
  must be recognizable as to their function and how they are to be
  manipulated solely from their appearance. These physical flight
  control systems cannot use interfaces such as a keyboard, mouse, or
  gaming joystick to control the aircraft in simulated flight.
B.3.1.2 Virtual controls are those controls used to set up certain
  aspects of the simulation (such as selecting the aircraft
  configuration, location, weather conditions, etc.) and otherwise
  program, effect, or pause the training device.

I have seen videos where the setup exceeds the requirements for the BATD but without a LOA it is not a BATD and time cannot be logged for purposes of fulfilling the experience requirements for certificates or ratings.
I have flown older BATDs like the ones that used to be sold by ASA and they don’t provide a very realistic flying experience. I used FlyThisSim extensively for IFR training and it does a pretty good job of simulating a real airplane. For IFR training X-Plane and my Mac are just as good. I haven’t tried either one for VFR maneuvers.


text:
Why would an aircraft drastically reduce in speed and then accelerate during landing?
I was on a flight today and I noticed that as we were approaching to land, the plane drastically reduced its speed for few seconds and then regained its speed.
Can somebody tell me why?

Speed is very difficult to observe from the passenger compartment. What makes you think you reduced speed and then regained it? Perhaps your question is answered here: If airplanes can't use reverse thrust in flight, what am I hearing?

Possible duplicate of If airplanes can't use reverse thrust in flight, what am I hearing?

You mean that G forces moved you forward, then back into your seat?

Even a sim can create this perception when you are sitting inside a box bolted to the ground and connected to hydraulic actuators.

Fun read: https://en.wikipedia.org/wiki/Sensory_illusions_in_aviation

Recently I was on an A320 that on final approach, not even 500’ AGL, suddenly pitched up sharply, sank, went to TO/GA power (you could hear the engines chainsawing), slammed the nose back down, and rolled back the engines.  I knew about the extreme pitch-up because I was looking out the window and had a clear visual reference for pitch.  But if I hadn't, and was only going by gee forces, I could have mistaken that for dramatically slowing down and speeding up.

Wind shear?  Have no experience of this in commercial aircraft, but in SEL it's not uncommon to encounter changing winds, and add throttle and/or pitch down to counter them.

Very interesting question:The inertia of the aircraft prevents the spoilers to reduce drastically in few seconds the speed of the aircraft, that’s typically a gust effect; the regain in speed is natural because the gust may change suddenly its direction, but the later speed increase could result too from the pilot who decided by precaution to increase the thrust suspecting a kind of slight wind shear. –

Could be the tiltback from the landing flare

@user40476 Hi i am a actually new to the aviation world so do you all have any resources or any links where i can learn all the things related to aviation and aircrafts . I am very entgusiastic about aviation and i would appreciate it greatly if you all could help me out

Your question uses the adverb "drastically". It's very unlikely that whatever happened was drastic. When an airliner does something drastic, it's a pretty memorable experience. In the absence of visual cues, some other sensations can be magnified in our experience, so it's quite possible that any change was less extreme than it seemed to be.
Sometimes, the plane is actually slowing down and speeding up. This could be in response to an air traffic control instruction, a not-quite-right adjustment that needs to be corrected, changes in local wind condition and so on.
It could also be that the plane needed a little adjustment after intercepting the glide-slope.
At this stage of its flight, the crew many need to respond to many different kinds of factors in its environment.
However, just because you had sensations of speeding up or slowing down doesn't mean that that is actually what happened. Changes in pitch can also produce these sensations, especially when combined with changes in engine sound.
In short, if that did actually happen, it could be for all kinds of reasons, but just as likely, it was an illusion.


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Why doesn't a full yoke deflection also change the stabilizer trim on the Boeing 737 MAX?
Various websites have stated that during the 737-MAX crash in Indonesia, the pilots could not pitch up because of a faulty AOA sensor pitching the plane down.
The stabilizer has a rear fulcrum and front jack screw. The elevator, positioned by yoke, is hinged to the stabilizer.
If the yoke is pulled back, the elevator moves up. Then the stabilizer must move down, either automatically or manually, to remove the yoke loading.
However, if the yoke is fully pulled back, why doesn’t this force the stabilizer down directly so that the pilot always has total control of pitch without checking the flight manual or pushing switches?

The yoke does move the elevators, whereas the trim moves the horizontal stabilizer. The stabilizer is much larger than the elevators, and therefore is more effective than the elevator at extreme angles. Even with full backpressure, the nose would continue to pitch down.

Nonetheless, all 737NGs/MAXs have trim cutout switches, 1 for the autopilot and 1 for the normal electric trim. Using these would immediately disable the electric trim. These are generally part of a standard trim runaway situation, but the crew did not recognize the situation and failed to use them.

+1 Good answer but IMO does not explain "why doesn't the yoke also move the elevator at yoke extremes (full forward and full back) so that pilots always have pitch control?". That's a good question IMO.

Because the yoke DOES control the elevator. The basis of the question is incorrect, the yoke does NOT control the Trim. In fact, the 737 does NOT have Trim Tabs, it has Servo Tabs for when the Flight Controls are in Mechanical Mode.

Note that the previous crew did use the switches. The condition already existed on PK-LQP during the flight (JT-43) preceding the accident one and the crew cut out the trim (shortly after take-off) and completed the flight. They reported all the various symptoms they had to maintenance, but the troubleshooting instructions failed to mention the possibility of them being caused by bad AoA probes, so maintenance didn't check it.

@RAC I think he is asking why isn't it designed with logic that if you have ran out of elevator, the stab starts moving in the same direction. I don't deal with autoflight much, but I think it uses a similar concept of control with the elevator but if it is holding an input for long it'll adjust the trim to unload the elevator.

The effectiveness of the stabilizer in comparison to the elevator is not simply a matter of size (surface area). The stab deflection range is much less than the elevator, which tempers its effectiveness.

On airplanes without flight envelope protection, the pilot needs to feel how much force they are applying to the flight control so they get a feel for how close to the edge they are getting. That is the reason for the regulation that requires the control force to increase linearly for each additional increase in pitch attitude — and the need for MCAS, which restored that linearity at very high pitch angles on the MAX (by de-trimming the elevator).
Accordingly, in manual flight, there is no auto trim. The pilot puts the airplane into the desired pitch attitude using the elevator, which deflects enough to provide ample pitch authority, and then must manually trim out the yoke force using the trim switch or trim wheel.
The autopilot auto trims soon after changing pitch with the elevator. This minimizes the chance that there will be a residual yoke force which the pilot does not (cannot) anticipate when the A/P is disconnected. Such residual force, suddenly released when relinquishing control to the pilot, is essentially an abrupt control input, which at best can be upsetting to passengers, at worst can cause injury, structural damage or loss of control. That is also why the A/P will not engage if it detects force is being manually applied on any of the controls. It is also why the first step in the stab runaway procedure is: Control wheel — grasp firmly; before turning off the A/P, as it likely had already begun using the elevator to counter the runaway.
If the stab were to work as suggested, holding the yoke at its stops would effectively start a stab trim runaway!

reconsider "pitch attitude"?

Reconsider to …?? With attitude meaning orientation, and described by pitch, bank and yaw angles, I'm used to specifying which axis is the relevant one when the attitude in the other two axes are irrelevant to the discussion. I think U.S. practice is to drop the word "attitude" altogether?

The stabiliser moves the elevator, not the other way around.

The elevator is for direct, high frequency and limited authority control of the aircraft attitude.
The stabiliser is for trimmed aeroplane position: release the stick and it will return to the zero force position, which is the stick trim, which should correspond to steady state flight.

With a released stick, if the trim switches are flicked the whole stabiliser - including the elevator hinge - moves and brings the elevator to a new neutral position. Also, the trim of the aeroplane changes. The elevator acts as a fast addition to aircraft trim, by design: trim is very powerful and should be slow and gradual, pilot pitch control must be able to provide fast pilot action.
The pilots may have good reason to trim the aeroplane fully nose down if for instance freight has shifted backwards. The B737 has Q-feel as mentioned in this answer, if they don't fly too fast they still have full elevator control with full nose-down trim.


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How to calculate the radius of wing tip vortices?
Is it possible to find the radius of wing tip vortices?

Welcome to aviation.SE. I removed the images, as they were not really needed for understanding the question.

Do you mean empirically, analytically or through numerical methods?

Measured from where? Vortices are conical

A vortex in free air does not have any sharp boundary, so it does not have an obvious definition of radius.
To get some general idea, consider how the vortex is formed: the wing accelerates the air downward, over all of its span—that is how it generates lift. Since the air outside the span is not moving down, the boundary becomes a vortex line and it starts at the wingtips. This is the wingtip vortex.
So the two wingtip vortices “touch” from the start, and therefore have radius of half span. As the air below gets pushed out, the outside part of the vortices starts moving up in width comparable to the inner part, though not as fast—the vortex as a whole moves down and a little bit inward.
This upward flow on the outside is used by many large migratory birds to save a bit of effort by flying in the V formations. The wing vortex of each follower partially cancels with the wing vortex of the predecessor, saving them a bit of energy. For the leader it is neither advantage nor disadvantage, but when it gets tired, it can fall back to the end of the flock and the next one becomes a leader.
Internal friction of air makes the vortex slow down over time, but also pulls in more air, so the affected area grows in size. There is no specific limit, it grows until it can't be detected anymore.
It is possible to calculate something precisely—so long as you can decide what to calculate (and what is it useful for so it is worth calculating)—but it requires powerful computer as the equations describing fluid motion, Navier–Stokes equations, don't have analytical solution.


text:
Can you please identify this aircraft from a BBC show?
The image is from:  BBC Skies Above Britain Series 1 "Flying into Danger" - Episode 1

"is there a website for aircraft identification?" Yes, this one :) We love aircraft identification questions here.

Unless it's obviously some bad photoshop where there's 20 jet engines on a cessna 172 @Bianfable.

@GdD For better or worse, we sometimes even deal with photoshops

I know @Jamiec, we don't love them though.

Although a little hard to read, the reg is F-BXCP which you can find with a search
https://www.airport-data.com/aircraft/F-BXCP.html
The aircraft is a Max Holste MH.1521 Broussard which is a 1950's era aircraft originally built for the French airforce.
Somewhat interestingly that aircraft is now registered G-HOUR and is owned by the luxury watchmaker "Bremont" (hence the reg). It seems to have first got a reg-change with the same paint scheme and then latterly been repainted.


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Which airfoil to use for high subsonic flight?
I am desigining an aircraft, which shall fly up to Mach=0.9 in cruise flight in an altitude of 10 km.
So when I think of which airfoil to choose, I have to consider aspects like

max. lift coefficient required
max. necessary/allowed angle of attack
...

But what comes first in my mind is, that I have to prevent shock waves forming on my airfoil, because drag will dramatically increase. So actually, this is my first demand for the airfoil.
NACA 64006 is a supercritical airfoil. In order to prevent Mach=1 on the airfoil, I would need a swept wing with an angle of more than 50° to reach Ma_crit=0.88 .
I am wondering now, if this is normal that I need such a high sweep angle? Or did I choose the wrong airfoil. So normal commerical aircraft have angles between 30 to max. 40° ?
So the only way to have less sweep angle: find another airfoil (I think 64006 is already one of the best free available airfoils)  or I accept higher values of drag coefficient ?
How do airliners tackle the problem? I think I read that they allow mach numbers a little bit higher until the drag divergence velocity?

For those high Mach numbers I would look at business jets. Commercial airliners rarely reach speeds of M0.9.
In addition, consider that commercial airliners don't use a standard NACA airfoil, but along the span of the wing the airfoil changes and the shape is quite a secret

NACA 64006 is not a supercritical airfoil. There are better choices. While not many have been published, any of those will be better than the old NACA. For a collection see here

Yes, you chose the wrong airfoil.
While the NACA 6-digit series was among the first set of airfoils computed from a design pressure distribution, they will suffer from shocks when operated above their critical Mach number just as any other airfoil.

Comparison of drag rise over Mach for 6-series and early supercritical airfoils from NASA Technical Paper 2969. It should be obvious which one is to prefer.
When transsonic research started, inverted airfoils paradoxically turned out to perform better at moderate lift coefficients and high Mach numbers than regular airfoils. Key is the low curvature on the suction side which makes a shock-free pressure rise possible. Practical designs aim for a weak shock over a range of lift coefficients. In oder to produce the most lift at a given Mach number, the pressure difference between upper and lower side can be maximized where thickness is low, i.e. in the rear area of the airfoil. This is called "rear loading". Supersonic flow on the upper side allows to create more lift over the full chord. On the most recent designs another small lift contribution results from a slower pressure drop on the forward edge of the lower side pressure distribution (the forward lower-surface undercutting of Phase 3 airfoils).

Effect of forward lower surface undercutting, from NASA Technical Paper 2969. The added lift at the forward part also lowers the pitching moment of supercritical airfoils.
Supercritical airfoils have negative camber over most of their forward part and strong positive camber only in the rearmost 20 - 30% of their chord. This NASA report (PDF!) lists a range of supercritical airfoils with different thicknesses and design lift coefficients. But it can only serve as a starting point since wing sweep will change the pressure distribution locally and demands a shift in the point of maximum thickness (forward at the root, backward at the tip) and more negative camber at the root in combination with a higher local incidence.
Mach 0.9 is only used by business jets where owners care more about bragging rights than fuel consumption. Airliners normally fly at Mach numbers ranging between 0.78 (short range) and 0.84 (long range) and for best efficiency should stay below Mach 0.82. They fly a bit above their drag divergence Mach until the gains in speed are balanced by the losses in drag. Of course, they can be operated at higher speeds but do so only to make up for a delay.

Thank you Mr. Peter Kämpf.

Thank you Mr. Peter Kämpf. So airliners don't use critical airfoils? And what if I want to fly at Ma=0.9 ? Then I should choose as "beginner" without any access to company secret details the mentioned supercritical airfoils of you? Is this the main design driver to avoid drag?

@Lucas Airliners use supercritical airfoils since the A310. Still, they prefer to fly a bit slower than Mach 0.9. Supercritical only allows to raise Mach a bit, or to use a thicker airfoil at the same speed. Or use less sweep at the same speed. Read the linked answers and all should be clear.

Dear Mr Kämpf, so I looked up :
https://ntrs.nasa.gov/api/citations/19900007394/downloads/19900007394.pdf
On page 70 (72 in pdf) the pressure distribution is plotted. So for alpha=0° the cp_min = -1,1   what is way lower than approx. cp_sonic=-0.35    . So the velocity on the airfoil is higher than Ma_crit . So why should this be a supercritical airfoil?
Can it only used together with negative angle of attack?

@Lucas It is a supercritical airfoil because it can tolerate higher than sonic (= critical) speeds without a shock. The very fact that velocity on the airfoil is higher than Ma${crit}$ without a strong shock makes it supercritical. Besides, $c{p;crit}$ is -0.65 if you talk of Fig. 36. Don't look at the figures only, please also read the text in the PDF.

OK Roger that, now deleting.


text:
Are noise cancelling headsets safe?
Headsets such as the Lynx Micro System are modelled on ear defenders and physically attenuate the noisy cockpit environment by clamping hard onto your noggin. Most modern GA headsets (e.g. Bose A20) seem to be built with far less attenuation, don't clamp on as hard, and tend to rely on ANR features rather than isolating the ear.
Naively, it seems that this would pump more audio power into the ear. Granted, it will be in opposition to the original noise, but it seems it would be very tricky to get the cancellation exactly in phase. So, is there a risk that using ANR and less attenuation would not be as effective in preventing ear damage as passive attenuation?

I'm voting to close this question as off-topic because this is purely an audio signals or physics related question.

I'm not sure I can make this question any more on-topic without changing the scope of the question. It's a question asked by a qualified pilot about cancelling noise in a noisy cockpit environment related to aviation. It seems to fall between the permitted or prohibited topics in http://aviation.stackexchange.com/help/on-topic
Granted, it is as much about audio or physics as aviation, but will they accept it at physics.stackexchange.com?

I doubt it'll be accepted on Physics, which is pretty selective, and not oriented day-to-day physics. But a Google is rather generous on this topic. Sample.

Headsets and the use thereof is very much an aviation topic. This question may also fit on other exchanges, but a headset is very much an integral part of the aviation experience. Many (most?) headsets are TSO'd aircraft equipment. I see this question as being on-topic just as much as other questions regarding aviation physiological factors or the function of aircraft parts and equipment.

We already have a question on how to choose a headset, surely a question specifically about the safety a subset of headsets is on topic.

Naively, it seems that this would pump more audio power into the ear. Granted, it will be in opposition to the original noise, but it seems it would be very tricky to get the cancellation exactly in phase.

If the headphones succeed in reducing the noise you hear, then they will also have succeeded in reducing the power delivered to your eardrum (at the relevant frequencies) -- because those are one and the same.
It is conceptually and mathematically convenient to imagine that the original noise and the canceling noise both reach your eardrums and interfere there -- but if you actually work out how energy moves in the combined situation, what actually happens is that the cancellation speaker sets things up such that much of the sound energy will get reflected away from your ear canal instead of entering it.
The core mathematical point is that the air displacements and minute pressure differences that make up the sound do indeed (to a good approximation) behave linearly -- so you can take a description of the noise and a description of the cancelling noise separately and simply add the displacements at the location of your eardrum.  But power goes as the square as the displacement, so it does not add linearly. You can't take the power transport of one sound along and add it to the power of another sound to get the power of the combination (except averaged over time if the sounds are not coherent in frequency, which is specifically not the case for noise-cancelling headphones).

Yes, they are safe for your hearing.
I've used them for about a decade, and the noise level is clearly lower with ANR than without. I've never seen any evidence that the energy they put out can damage one's hearing; by every account, rather, they do a good job protecting your hearing from the damaging effects of hours in a noisy environment.

I also have used ANR headsets for over a decade and still have excellent hearing, something I particularly note with the high frequency range (17-20+khz).


text:
Could sprinkling cool water on the runway in hot summer decrease air density?
Why is there no such technique used where cool water gets sprinkled on a runway?
Cooling down the air above the airport would decrease air density and therefore lead to a shorter starttime for airplanes.
This image explains exactly what I mean.
(related article: https://www.boldmethod.com/learn-to-fly/performance/prevent-a-density-altitude-crash-on-takeoff/)

Humid air is less dense than dry air. The drop in temperature has to compensate for that. The biggest drop is possible if evaporation happens right before air is ingested by the compressor. That function is performed by water injection for improving thrust in hot and high conditions.

What happens when the aircraft can't climb out of the more humid/cooler air because the hot air is just above it?

Why would you want to decrease density? That's backwards.

Another problem is now your balanced field length takeoff plus landing performance has to be based on "wet runway" parameters which adds significant penalty, more than negating any benefit you got from evaporative cooling.
Now if you were in the desert you might get some kind of benefit with a fogging system that blew atomized water fog over the runway where it evaporated immediately without making the surface wet, like is done with outdoor terraces at bars.  The temperature drop from that evaporation might give some tiny performance benefit.  If you could find someone to pump all that water along a 5000 ft runway, at the water utility rates you'd be paying in a desert environment.

It would be a lot cheaper to remove cargo (people/baggage) to be within performance limits for hot/high operations than to create a weather pattern around an airport for the purpose of taking off (and possibly crashing as they may not be able to climb out of the hot air)

Actually it made me think of it as kind of the inverse of this wild and crazy concept that was used quite a lot in WW2 https://www.youtube.com/watch?v=gAIjxaJ2_Ag  You sure has hell wouldn't want to drift off to the side!

There are a few problems with this idea:

The water evaporating would increase the humidity, likely canceling any cooling benefit.
The effect would be localized in a very small region just above the pavement.
The effect would be temporary as any breeze would quickly blow the cooled air away.


text:
Is it fact or fiction that Ashgabat control tower is misplaced?
It's often written that the construction of Ashgabat International Airport was sabotaged by the aesthetic whims of the country's late leader, Saparmurat Niyazov.  The story goes that Niyazov, presented with the architectural plans for the airport, insisted that the air traffic control tower be moved to the "wrong side of the runway".  He supposedly overruled the better judgment of the airport planners because he thought the airport would look better that way.
In the West, Niyazov is widely considered to have been an eccentric and megalomaniacal dictator, thanks in part to stories like this.  While many of these stories are undoubtedly true, others have been shown to be exaggerations or misinterpretations.  I'd like to know whether there's any truth to the story of Ashgabat's air traffic control tower, or if it's just another one of the false but plausible-sounding rumours cooked up to further mock Niyazov.  So my questions are basically as follows:

Is there, in fact, any significant problem with the placement of the air traffic control tower at Ashgabat International Airport?
If the tower is poorly placed, what specific problems does this placement cause for air traffic controllers and airplane pilots, and how do they work around these problems?
If the tower is poorly placed, is there any reliable evidence that this was a result of Niyazov's direct personal involvement?  If there isn't, what's the earliest known appearance of this claim?

I don't see much wrong with the tower right behind the terminal. It is also between the airport's two runways.

Although this is certainly aviation-related, your questions 1 and 3 seem like they might be a better fit for skeptics.SE.

Useful links: Aerodrome chart from AIP Russian Federation // Airport on SkyVector // Aerial view on Google Maps. From the aerodrome chart, and the Maps view, it seems the tower is well located and has a good view on the runways, though view on 12R threshold must be confirmed vs tower height

There are videos on Youtube, including this one. From this video, it seems the tower -- here at the top left corner -- is quite tall and the view shouldn't be obstructed by constructions and hangars. Note the tower is at the center of the airport and both runways, not at "a wrong side of a runway".

What, specifically, does that book say about the tower, and where does the author get the information from?

@Pondlife: Point taken about #3, but question #1 is better answered by aviation experts than by skeptics with no particular knowledge of airport design.

@Psychonaut A few of us do have accounts over there.

Although this is certainly aviation-related, confirming or refuting rumours is a speciality of https://skeptics.stackexchange.com/.

It would seem your question ends with the first part. Having checked out the airport online, checking images, maps, etc, I can't see anything wrong with the placement of the tower. It actually seems nearly optimal... It's very near the center of the airport with an unobstructed view of the whole facility, and between the 2 main runways....  Parts 2 and 3 of your question become non-operative, so yes, this is a valid question here, and need not be sent to a skeptics group.
What was interesting to me though was that the image in google maps satellite view seems to show the parking spaces around the tower completely empty... No controllers on duty the day the image was taken?

Maybe they use taxi :p makes sense considering the number of taxiway there is

There are also almost no planes and lots of construction work going on: perhaps the airport wasn't yet operational?

No planes? In the image I see the terminal has plenty of planes at the gates, but no cars at the tower.... I had thought it might have been early morning, but the tower shadow is showing just before noon.


text:
How many displays does an ARTCC Air Traffic Controller view and what is displayed on each?
I am trying to figure out the relation between the data sent to a center (ARTCC = Air Route Traffic Control Center) air traffic controller and the displays they view. Did the workstation change when En Route Automation Modernization (ERAM) was implemented?
I am really just looking for a general description of a center air traffic control workstation (if it varies based on the type of controller I would like to know any significant differences).

I recommend finding an "Operation Raincheck" at a Center or Tower near you.  It is a program run by the FAA to give "civilians" (primarily pilots) an inside tour of a ARTCC or Control Tower.

Although your question is specifically about the USA, I thought an insight into a typical European setup would be interesting as well. I imagine it will be very similar to what you find in many American centers.

The image is from Copenhagen Area Control Centre (Denmark) and shows a normal controller working position. You will notice five screens in total.
The largest screen, immediately in front of the controller, is the main situational display. It is essentially the radar screen, showing different aircraft in their geographical position in relation to airspaces and other traffic. Typically, the situational display will also, depending on the specific system, enable the controller to interact with aircraft labels, for instance to enter notes about clearances and instructions and show them directly on the display.
To the left is a secondary screen which also shows information about traffic in the area. Here, the traffic is presented in text lists, which allows the controller to get a thorough overview of what is currently going on, and what is coming. This is basically a replacement for old fashioned paper flight strips (which are being phased out across the world). In this example, it also features the arrival management (AMAN) system.
Below the main situational display there are three screens. From left to right, the first one is a telephone panel, which gives the controller easy access to all relevant phone communication lines. It is a touch screen, and by pressing any button on the screen, the controller can call adjacent ATC sectors, control towers, emergency services, the meteorological office etc. to coordinate.
The lower middle screen can show a lot of different information. On the image above, it is set up to show the frequencies of other ATC sectors in the area along with any active military areas. It can also be used to retrieve meteorological information or anything else that might be relevant.
Finally, in the lower right corner is the voice communication system (VCS) interface. Also a touch screen, here you have control buttons for the VHF radio equipment, used to communicate with aircraft. The controller will be able to toggle which radio frequencies are used to transmit and receive, and will receive information about any radio equipment that might not be working as it should.
Apart from the actual computer screens, you will notice the backup phone to the left and a clock above it. There is also a backup VHF radio in the upper right of the console, but that cannot be seen on the above image.

J. Hougaard - excellent post - where did you source this image from? I'm writing my thesis and would love to include it, but obviously want to give correct attribution and/or obtain permission for use.